Study On Control Of Pyrite Oxidation At Source

Under wetted ,dried and flooded conditions ,the mechanism of pyrite oxidation was studied using column leaching experiment both at 30℃ and at natural room temperature and shaking culture experiment at 30 ℃. The possibility and optimum conditions of coating formed on pyrite surface and its role in controlling further oxidation of pyrite were conducted utilizing the methods of kinetics ,electrochemistry and simulation of column leaching , especially for comprehensive control of pyrite oxidation.The results showed that bacterium thiobacillus ferroox idanis plays a decisive role in oxidation of pyrite. After pyrite in the column was leached circularly for 360 days at the natural room temperature, the percentage of pyrite oxidation inoculated with T. F was 5. 32%,but 0. 21% for the non-inoculated (CK ). The pH value in the former leachate dropped from 7. 55 to 2,35, but from 7. 60 to 6. 10 for the letter. After pyrite (30g) was leached circularly for 143 days at 30℃ under wetted condition,the accumulation of SO42- in the leachate rose up to 4690mg for inoculated sample and 182mg for noninoculated one. Temperature exerted strong effect on pyrite oxidation caused by T. F and 30℃ was the optimum temperature for the T. F growth. Also,Fe3+ could oxidize the pyrite ,but it was weak in comparison with T. F. This showed that T. F took direct attack on pyrite. The rate of pyrite oxidation resulted from chemical reaction was low and changed little,but that resulted from T.F underwent the adaptive and the accelerative periods,which presented only under wetted condition. No difference in oxidation rate between the inoculated and the noninoculated exsited under dried and flooded conditions- In addition,the order of pyrite chemical oxidation was: the wetted >the dried>the flooded. Pyrite oxidation had relation to Eh. The higherEh,the faster pyrite oxidation. Eh>0. 60V vs. SHE (standard hydrogen electrode) indicated that fast oxidation of pyrite took place. Eh 0. 60V seemed to be the critical value for pyrite speedy oxidation.When pyrite was leached with the solution containing 0. 10mol · L-1 H2O2 and 0.01mol · L-1KH2PO4 or with 0. 1mol· L-1 H2O2 and 0. 05% 8-hy-droxyquinoline at pH3,5 and 7, the coatng formed on the pyrite sueface, which could suppress the further chemical oxidation of pyrite effectively,especially at pH5.The effect of coating was dependent on the temperature and the concentration of H2O2,which was not the same between KH2PO4and 8 — hydroxyquinoline. Temperature rising from 25℃ to 40℃ was good for 8-hy-droxyquinoline and no effect on KH2PO4. The H2O2 concentration raised from 0. 1 mol ·L-1 to 0. 2mol · L-1 was not good for KH2PO4 and no effect on 8-hydroxyquinoline. The reaction between H2O2 and pyrite obeyed to pseudo zero order.Electrochemical behavior of pyrite was studied using voltammetry. Very low currents were observed in the voltammograms of pyrite electrodes during the anodic scan from 0. 15 to 0. 85V vs. SHE,indicating no anodic oxidation taking place. Above 0. 60V vs. SHE , an expotential increase in current emerged,indicating initiation of pyrite oxidation. When the pyrite electrodes were treated with the two solution mentioned above for coating,the anodic current became weak obviously. The results showed that the coating on pyrite surface could suppress the electrochemical oxidation of pyrite effectively. But, the coating could not stop the pyrite oxidation to take place, which was dependent on the quality of coating and impurity on pyrite surface.That FePO4 coating on pyrite surface could not control the biological oxidation of pyrite caused by bacterium T. F was confirmed using the simulation of column leaching. Conversly,FePO4 coating accelerated the biological oxidation of pyrite. Perhaps ,PO43- helped the T. F growth and electron transfer during using the energy materials. Iron - 8-hydroxyquinoline coating pub-lished first in the thesis not only controlled the chemical oxidation like FePO4 coating but also suppressed the T. F growth like bactericide. So, it presented remarkable effect on control of pyrite oxidation under the wetted and the dried conditions. The percentage of pyrite oxidation treated with 8-hydroxyquinoline only accounted for 2. 9% of the inoculation (CK) after pyrite in column was leached circularly for 360 days at natural room temper-ture;2.2% under wetted condition and 25% under dried condition for 143 days at 30℃. Iron -8-hydroxyquinoline coating proposed in the thesis provided a novel approach to control of pyrite oxidation at source by combining coating with bactericide and development of the solid bactericide with low solubility and low mobility.